| Titanium alloys have outstanding properties of high specific strength, high temperature properties and exceptional corrosion resistance. However, titanium alloys suffer from the serious disadvantages of poor tribological properties, which prevent them from being widely applied. Surface treatment techniques are very effective ways to improve titanium alloy's tribological properties. Ion nitriding, physical vapour deposition and ion-implantation techniques etc. can be used in low-medium loading and sliding velocity condition. However in high loading and sliding velocity condition the surface-modification layers are easily destroyed because of their poor load-bearing capacity and bonding strength. In addition, there are impact and corrosion etc. apart from friction and wear at the same time in many important application fields. The all-around properties of titanium alloys need to be improved. To solve these problems, this paper proposed to form Mo and Mo-N surface-modification layers on Ti6A14V alloy by double glow plasma surface alloying technique. The component and structure, mechanical properties, tribological properties, corrosion-wear behaviors and corrosion properties of Mo and Mo-N surface-modification layers have been studied. The main results have been obtained as follows:(1) The component and structure of Mo and Mo-N surface-modification layer of Ti6A14V have been studied. The modification layer is a duplex layer, composed of diffusing layer and surface coating. The surface coating changes the properties of Ti6A14V's surface completely. The diffusing layer in which the chemical components and hardness change gradiently can enhance load-bearing capacity to the coating and ensure the durability of the coating. The test results show that temperature is an important parameter in forming the diffusing layer. The surface-treatment temperature should be about 900℃ in order to form diffusing layer with enough thickness without damaging the mechanical properties of the substrate. The flux ratio N2/Ar is an important parameter for fabricating Mo-N modification layer. The component and structure of Mo-N modification layer has been studied at different flux ratio N2/Ar.(2) The nano indentation and microhardness tests show that Mo and Mo-Nmodification layers enhance the surface strength of Ti6A14V substrate. The average values of hardness and elastic modulus of Mo modification layer fabricated at 900℃ are 10.86GPa and 278.84GPa, 3.76 times and 2.50 times as that of Ti6A14V substrate respectively. The average values of hardness and elastic modulus of Mo-N modification layer fabricated at 900℃ and flux ratio N2/Ar=1 are 13.80GPa and 261.65GPa, 4.78 times and 2.35 times as that of Ti6A14V substrate respectively.Bonding strength is evaluated by indentation, scratch and impact tests. Mo modification layer shows the best bonding strength because of its high toughness. It is important to adjust hardness and toughness of the modification layer under some application conditions.(3) The tribological properties and mechanism of the modification layers have been studied by ball-on-disc test. Mo modification layer and Mo-N modification layer all increase the wear resistance of Ti6A14V substrate remarkably. Under unlubricated condition, Mo modification layer shows the best wear resistance when the countpart is GCr15 ball. When the countpart is corundum ball, Mo-N modification layer shows the best wear resistance. The excellent wear resistance of Mo and Mo-N modification layers comes from their strong enough load-bearing capacity and bonding strength. Under lubricating condition, 30* machine oil shows no obvious boundary lubricating for Ti6A14V because of its strong adhesive behavior, but Mo modification layer, Mo-N modification layer and nitrided layer all have low coefficients of friction and high wear resistance.(4) Mo and Mo-N modification layers all improve Ti6A14V's fretting-wear resistance, among them Mo-N modification layer has lower coefficient of friction and excellent fretting-wear resistance...
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